1. Field of the Invention
This invention relates to a universal washing apparatus, and in particular a washing apparatus for use in washing wells provided in reaction containers such as wells of microtiter plates, microcups and the like containers designed to hold samples or reagents used for chemical, immunological and other reactions.
2. Description of Related Art
Certain laboratory operations require the testing of small samples such as immuno assays which are carried out in an arrangement of microwells or wells having volumes of, for example, 50-300 microliters or less formed in microtiter plates, hereinafter referred to generically as well plates. An example of this type of laboratory operation is an enzyme linked immunosorbent assay or "ELISA" reaction which is performed for measuring antigens and/or antibodies.
Reactions of this type involve the adding and removing of liquid reagents within each well. At several stages of the reactions, the unbound liquid remaining in the wells must be removed and the inside of the wells must be washed by dispensing a wash solution such as water, a buffer solution, or other fluid in the wells using a gravity feed or a pump, and then evacuating the liquid under a vacuum.
The wells can be arranged in a strip or in-line format, or can be arranged in a matrix format. Until recently, commonly used matrices were configured to have 8.times.12 wells spaced at 9 mm apart between centers, hereinafter referred to as a 96-well plate. FIG. 1 illustrates a 96-well plate 1 having wells 2. However, with the advent of high throughput screening ("HTS"), two more matrixes were introduced which increased the total number of wells while keeping the overall size of the well plate the same: 1) the 384-well plate 3, as shown in FIG. 2, configured to have 16.times.24 wells 4 spaced at 4.5 mm apart between centers, and 2) the 1536-well plate configured to have 32.times.48 wells spaced at 2.25 mm apart between centers (not shown). Since the overall size of these new well plates are the same as the 96-well plate 1, the size of the wells in the new well plates is necessarily smaller than those in the 96-well plates while the depth of the wells remains the same.
A conventional washer used for removing the unbound contents in wells of a well plate includes dispense pipes for dispensing the wash solution into the wells of the well plate (e.g., by a pump or gravity feed), and aspirate pipes for evacuating the solution from the wells of the well plate (e.g., by a vacuum or a suction device). In order to quickly wash the well plates, the washing process is performed simultaneously on as many wells of the well plate as possible. A commercial example of such a washer is the SLT-LABINTRUMENTS 96PW washer.
Washers for cleaning the 96-well plate are well known. The conventional multi-well washing apparatuses of this type are constructed so that the dispense and aspirate pipes are connected to the same manifold body. When performing a wash operation, the wash solution enters the dispense portion of the manifold and gets channeled to the dispense pipes. Accordingly, the purpose of the dispense portion of the manifold is to distribute uniformly the incoming wash solution among the respective dispense pipes. The contents of the wells are then evacuated by the respective aspirate pipes into the aspirate portion of the manifold. Accordingly, the purpose of the aspirate portion of the manifold is to channel the wash solution from all the aspirate pipes into a common waste line.
Conventional washing apparatuses generally fall into one of two configurations which define the arrangement of the dispense and aspirate pipes:
1. the pipe-within-a-pipe configuration, as disclosed in (U.S. Pat. No. 4,635,665) and further illustrated in FIG. 3, wherein the dispense pipe 7 is disposed inside the aspirate pipe 6 such that the tips of both pipes at their respective open ends are disposed approximately in the same horizontal plane; and PA1 2. the pipe-next-to-pipe configuration as shown in FIG. 5 wherein the dispense pipe 11 is disposed adjacent to the aspirate pipe 10 so that both pipes fit within a single well 2, and wherein the dispense pipe 11 is slightly shorter than aspirate pipe 10 by a distance .delta. (e.g., by 1-3 mm). PA1 1. the ability to wash wells using an overflow wash operation for vigorously washing the wells, PA1 2. the ability to place an evacuation pipe in any or multiple places within each well to effectively evacuate the contents of the wells, and PA1 3. the ability to wash wells having a relatively small diameter such that only a single small aspirate pipe can be placed within the well such as those found in the newer well plates.
U.S. Pat. Nos. 3,849,830; 4,015,942; 4,559,664; 4,685,480; 5,078,164; 5,105,842; 5,186,760; 5,264,042; and 5,636,647 are additional examples of washing apparatuses and are incorporated herein by reference.
The foregoing two conventional washing apparatus configurations were created for use with the 96-well plate having 6 mm diameter wells. The pipe-within-a-pipe configuration has an outer pipe diameter of approximately 3.5 mm, and the pipe-next-to-pipe configuration has approximately 2.5 mm between pipe centers with each pipe being approximately 1 mm in diameter. Thus the overall dimension of the pair of pipes which enter a well during an evacuation process is less than the well diameter of a 96-well plate. However, the diameter of the wells in the new 384-well plate measures about 2.5 mm at the bottom of the well, and the diameter of the wells in the 1536-well plate is even smaller. Therefore, due to the smaller size wells, none of the conventional washing apparatus configurations described above can be used to evacuate the smaller wells of the 384- and 1536-well plates.
Next, different types of wash operations will be described with reference to the two conventional washing apparatus configurations described above.
An overflow wash operation occurs when the volume of wash solution dispensed into each well exceeds the capacity of the well and the excess wash solution is evacuated from the well by the aspirating pipe. Overflow washing is important when vigorous washing of the wells is required for successful removal of unbound material in the course of some reactions.
The two conventional washing apparatus configurations do allow for overflow washing of the standard large wells of the 96-well plates. However, as shown in FIG. 4, in the pipe-within-a-pipe configuration the overflow wash capability is limited due to the possibility of the suctioning off of the wash solution directly from the dispense pipe before the wash solution enters the well. This is particularly a problem when the dispense pipe dispenses the wash solution at low fluid delivery rates.
In the case of the pipe-next-to-pipe configuration as shown in FIG. 5, the overflow washing capability of large 96-well plates is improved due to the greater distance between the tips of dispense pipe 11 and aspirate pipe 10 which reduces the possibility of suctioning off the wash solution 8 before it is dispensed within the well 2.
On the other hand, the pipe-within-a-pipe configuration, is capable of performing what is known in the industry as a "bottom sweep" evacuation wash operation wherein the aspirate pipe 6 is positioned sequentially in several areas of the large 96-well plate wells close to the side walls for efficient evacuation.
However, as shown in FIG. 6, the ability of the pipe-next-to-pipe configuration to perform an efficient evacuation or bottom sweep of the well is restricted because the dispense pipe 11 limits how close the aspirate pipe 10 can be positioned to the inner wall of the well 2.
Attempts have been made to resolve the bottom sweep evacuation limitation of the pipe-next-to-pipe configuration. For example, as shown in FIG. 7, the dispense pipe 15 was made shorter than the aspiration pipe 14 by a distance slightly larger than the depth of the well 2. However, as shown in FIG. 8, this resulted in considerable splashing of the liquid being dispensed from the increased height position relative to the well 2, and the possible contamination of adjacent wells.
Thus, the foregoing conventional washers have limitations in washing conventional 96-well plates.
Furthermore, the recent introduction of the new well plates defined by larger matrices (i.e., the 384- and 1536-well plates) having narrower wells positioned closer to each other brought to light another limitation of the foregoing conventional washers. Namely, as noted above, the pipe-within-a-pipe and pipe-next-to-pipe configurations are adapted for washing relatively large diameter wells which are not available in the more recent well plates with the larger matrices. While the shortened dispense pipe 15 shown in FIG. 7 would permit the use of a conventional washer to aspirate the smaller size wells of the new well plates, the resulting splashing of liquid makes its use impractical since the contents of one well may splash into adjacent wells and contaminate them. Therefore, the conventional washers cannot be used with the newer well plates.
As shown in FIG. 9, one proposed solution that came to market for washing well plates having the new smaller well geometries is to provide a separate dispense manifold 19 having dispense pipes 20 and an aspirate manifold 17 having aspirate pipes 18 positioned in two separate locations next to each other. According to this design, the well plate 3 is first presented to the dispense manifold 19 for dispensing the wash solution, and, next, moved to the aspirate manifold 17 for the evacuation of the unbound contents in the wells 4. One commercial example of such a washer is the SCATRON EMBLA 384 model. While the small aspirate pipes 18 of this split manifold design are able to fit into the smaller new wells 4, the design can not be used to perform overflow washing of wells. Furthermore, the additional time required to move the well plate (or manifolds) between the dispense position and aspirate position is long, thereby reducing the efficiency of the washing operation. Moreover, the overall dimensions of an apparatus having this design is necessarily large.
Accordingly, the foregoing conventional apparatuses have one or more shortcomings in that they are not able to provide simultaneously within the same apparatus: